It's no surprise that mutual admirers Pat Metheny and Brad Mehldau had an instant musical rapport when they got together in late 2005 to record their first joint album. What is surprising, though, is that it took these two jazz stars more than a decade to team up for the sessions that produced last fall's acclaimed "Metheny Mehldau" CD and its just-released sequel "Quartet."

"It's funny," said Metheny. "Because among musicians there's this kind of typical sign-off, the equivalent of 'We should do lunch sometime' in the civilian world. The musician equivalent is: 'We should play together sometime.'

"And when Brad came on the scene, I was such an enthusiastic fan; I was so hungry to hear somebody play like that. Then, I saw interviews where he cited me as an influence, which was very flattering. But so many of the things I aspired to do, musically, I can hear Brad aspiring to, and doing, too."

Their compatibility is immediately evident.

Mehldau's absorbing improvisational approach is matched by his melodic depth and harmonic ingenuity. At 36, he is one of the most eloquent and original pianists of his generation - and one of the most popular. His supple keyboard touch and emotional intensity make him a perfect foil for Metheny, 52, one of jazz's most eclectic and influential guitarists.

Still, it wasn't until he had a night off during a 2005 summer tour of Europe that Metheny, who says he performed 200 gigs that year, had a chance to spend more than a few minutes with the equally busy Mehldau.

It was then the two realized the only way to ensure a collaboration would be to formally schedule a recording date. Neither knew what direction their project would take, but when they got together in New York that December they'd written more than 20 pieces of music.

"It's difficult to describe how quickly it came together," Metheny said by phone from New York. "The version of (the lattice-like ballad) 'Unrequited' on the first album was the first time we played it.

"We started playing through all this music and some tunes had different challenges. But we walked out with an enormous amount of music. There are tracks we cut that haven't come out on either album."

Mehldau's ace rhythm section of bassist Larry Grenadier and drummer Jeff Ballard appears on both albums. But they are more prominently featured on "Quartet," which finds Metheny using four distinctly different guitars and a guitar synthesizer on the album's five opening cuts alone.